The present invention relates generally to fuel limiting strategies for internal combustion engines, and more specifically to such systems for controlling engine exhaust temperatures during engine operation.
When combustion occurs in an environment with excess oxygen, peak combustion temperatures increase which leads to the formation of unwanted emissions, such as oxides of nitrogen (NOx). This problem is aggravated through the use of turbocharger machinery operable to increase the mass-of fresh air flow, and hence increase the concentrations of oxygen and nitrogen present in the combustion chamber when temperatures are high during or after the combustion event.
One known technique for reducing unwanted emissions such as NOx involves introducing chemically inert gases into the fresh air flow stream for subsequent combustion. By thusly reducing the oxygen concentration of the resulting charge to be combusted, the fuel burns slower and peak combustion temperatures are accordingly reduced, thereby lowering the production of NOx. In an internal combustion engine environment, such chemically inert gases are readily abundant in the form of exhaust gases, and one known method for achieving the foregoing result is through the use of a so-called Exhaust Gas Recirculation (EGR) system operable to controllably introduce (i.e., recirculate) exhaust gas from the exhaust manifold into the fresh air stream flowing to the intake manifold. valve, for controllably introducing exhaust gas to the intake manifold. Through the use of an on-board microprocessor, control of the EGR valve is typically accomplished as a function of information supplied by a number of engine operational sensors.
While EGR systems of the foregoing type are generally effective in reducing unwanted emissions resulting from the combustion process, a penalty is paid thereby in the form of a resulting loss in engine efficiency. A trade-off thus exists in typical engine control strategies between the level of NOx production and engine operating efficiency, and difficulties associated with managing this trade-off have been greatly exacerbatedby the increasingly stringent requirements of government-mandated emission standards.
In order to achieve the dual, yet diametrically opposed, goals of limiting the production of NOx emissions to acceptably low levels while also maximizing engine operational efficiency under a variety of load conditions, substantial effort must be devoted to determining with a high degree of accuracy the correct proportions of air, fuel and exhaust gas making up the combustion charge. To this end, accurate, real-time values of a number of EGR system-related operating parameters must therefore be obtained, preferably at low cost. Control strategies must then be developed to make use of such information in accurately controlling the engine, EGR system and/or turbocharger. The present invention is accordingly directed to techniques for controlling engine operation to maintain engine exhaust temperatures within desired operating limits.
The foregoing shortcomings of the prior art are addressed by the present invention. In accordance with one aspect of the present invention, a system for determining engine exhaust temperature comprises a temperature sensor producing a temperature signal corresponding to a temperature of an intake manifold of an internal combustion, an engine speed sensor producing an engine speed signal corresponding to a rotational speed of the engine, means for determining a charge flow value corresponding to a mass flow of charge entering the intake manifold; and a control circuit producing a fueling command for fueling the engine, the control circuit responsive to the fueling command, the temperature signal, the engine speed signal and the charge flow value to estimate an engine exhaust temperature.
In accordance with still another aspect of the present invention, a method for determining engine exhaust temperature comprises determining a temperature of an intake manifold of an internal combustion engine, determining a rotational speed of the engine, determining a mass flow of charge entering the intake manifold, determining a fueling command for supplying fuel to the engine, and estimating an engine exhaust temperature based on current values of the fueling command, the temperature, the rotational speed and the mass flow.
One object of the present invention is to provide a virtual sensor operable to estimate engine exhaust temperature based on existing engine operational information.
Another object of the present invention is to provide a model-based strategy for estimating engine exhaust temperature.